The present invention relates to arrangements or systems for adjusting certain components of photographic apparatus or the like, for example, to arrangements for adjusting the diaphragm of a camera or copying machine or to arrangements for focusing the objective of a slide projector so as to ensure that the image of a slide is properly imaged on the screen. More particularly, the invention relates to improvements in arrangements or systems wherein an electric motor is controlled by a circuit including at least one photosensitive element and serving to move the motor to an extent (e.g., through a given number of revolutions) such that the component or components which receive motion from the motor automatically assume predetermined optimum positions. Still more particularly, the invention relates to improvements in arrangements wherein the component or components which require adjustment vary the electrical value of the photosensitive element until the circuit including the photosensitive element assumes a balanced condition or state which corresponds to the desired predetermined optimum position of the adjustable (mobile) component or components.